The present invention relates generally to operations performed and equipment utilized in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a formation isolation valve for use in underbalanced drilling applications.
A formation isolation valve is typically used in underbalanced drilling operations to close off flow through a casing string while tripping a drill string, or otherwise when access to a wellbore below the valve is not required. The valve is opened when the drill string or other assembly (such as wireline tools, coiled tubing string, etc.) needs to be displaced downwardly through the valve. The valve is then closed when the assembly is displaced upwardly through the valve.
Some formation isolation valves are operated hydraulically using control lines which extend to the surface. Pressure applied to the control lines at the surface is used to open and close such valves. However, these long control lines have significant disadvantages. For example, long control lines are expensive to purchase and install, long control lines have increased susceptibility to damage during installation and leakage thereafter, etc.
Some formation isolation valves are operated by physical contact between the valve and the assembly as it is displaced through the valve. The assembly may engage and shift a sleeve or other device which causes a closure member of the valve to open. This physical contact has the disadvantage that it usually requires relatively small clearance between the valve and the assembly, which leads to a restriction in the interior of the valve.
Therefore, it may be seen that improvements are needed in the art. It is one of the objects of the present invention to provide such improvements. These improvements may also be useful in applications other than formation isolation valves for underbalanced drilling.